Issue 24

A.Yu. Fedorova et alii, Frattura ed Integrità Strutturale, 24 (2013) 81-88; DOI: 10.3221/IGF-ESIS.24.08

The test conditions comply with the conditions of the experiment described in detail in [12]. Investigation of the heat source evolution was carried out on the smooth specimens during a quasi-static tensile test. Crack propagation was studied at loading frequency of 5 Hz and 10 Hz. The temperature evolution was recorded by an infrared camera FLIR SC 5000. The spectral range of the camera is 3-5 mm. The maximum frame size is 320×256 pixels; the spatial resolution is 10 - 4 meters. The temperature sensitivity is from 25 mK to 300 K.

(a) (b) Figure 1 : Geometry of specimen ( a – smooth specimen, b – specimen with a hole). All sizes are in millimeters.

E XPERIMENTAL DATA PROCESSING AND STORED ENERGY DETERMINATION

Post experimental data processing t the beginning of the data processing procedure, the first frame was subtracted from the film to eliminate the influence of infrared camera lens radiation on the temperature field. To increase data accuracy and to eliminate the influence of random temperature fluctuations, the spatially fixed temperature signal of the smooth specimen was processed using the two-dimensional discrete Fourier transform with a standard Gaussian kernel [13]. The result of such data processing used to calculate the heat source field is illustrated in Fig. 2. The relative motion of the specimen with cracks and the infrared camera lens observed in cyclic tests causes the problem of motion compensation, which should be overcome to obtain the correct temperature data at the given point on the specimen surface. To compensate this relative motion, the algorithm described in detail in [13] was used. The main idea of the algorithm consists in finding a marker zone on the examined surface and searching for this area on the surface in each time step. Further, the displacement of every point on the surface is calculated for each time step. The data processing yielded the temperature increment field (Fig. 3), which was used to determine the heat source field. A

(a) (b) Figure 2 : Infrared image of the smooth specimen before data processing (a) and the obtained temperature change field (b) .

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